# Reference Frame

1. Dec 3, 2004

### mani

Under "Dynamics", an Inertial frame of Reference can be defined absolutely as one that does not use "pseudo" or inertial forces.
Under "Kinematics" how do we define absolutely (any) "Frame of Referaece"?

2. Dec 4, 2004

### mani

"Reference Frame"

How is a "Reference Frame" defined absolutely (i.e. without introducing another Frame) under Kinematics ?

3. Dec 4, 2004

### ZapperZ

Staff Emeritus
Er... the moment you say "I'm going to measure the position of everything with respect to this point here", then you have defined a reference frame. An "inertial reference frame" will have a more stringent constraint than that.

Zz.

4. Dec 5, 2004

### cepheid

Staff Emeritus
David J. Griffiths offers some insights in his Introduction to Electrodynamics

I don't see how it makes a difference whether you are working with kinematics or dynamics; both are just aspects of classical mechanics, in which this definition applies.

5. Dec 5, 2004

### cepheid

Staff Emeritus
6. Dec 6, 2004

### mani

"I don't see how it makes a difference whether you are working with kinematics or dynamics;"

Kinematics is "Space" (or Geometry) + Time; where we can talk about moving "points"only.
Inertia is a concept that comes with matter under Dynamics.
Rotation can be detected only with inertia.

7. Dec 7, 2004

### rayjohn01

frame

As I understand it a 'frame of reference' is not dependant on the system considered per se, it is a set of values given to any and all variables within the system at some initial condition , and hence a referential situation.
To me dynamic and kinematic are the same thing involving motion , they may or may not involve rotation , which is a dimension , not included in inertial frames .
You must define carefully which variables you include or not -- then apply values to them as a reference 'point' ( multidimensional ).
To reply to whoever -- rotation has nothing to do with inertia -- inertia in the rotational sense is clearly due to momentum but momentum is the resistance to change in whatever direction in space. Rotation of zero mass does not involve momentum , it could be just the frame of reference ..
Ray.

Last edited: Dec 7, 2004
8. Dec 14, 2004

### mani

That was a bit above my head!
In kinematics, i can take a "rigid" set of points as a Frame, if someone can assure me that it is not rotating but moving only translation. If any other set of points is moving only in translation w.r.t. the above "certified" frame, that also can be accepted as a frame.
Absolute rotation of only a material frame can be detected by the inertial forces